1. Field of Invention
The present invention relates to a lamp lighting device and a filament lamp used, for example, for the heating of semiconductor wafers.
2. Description of Related Art
Light irradiation type heating devices in semiconductor production processes are utilized over a broad range of film forming, diffusion, annealing etc., and in each of these treatments a plate-shaped object to be treated such as a semiconductor wafer can be heated rapidly. The temperature is increased to 1000° C. and more within some seconds to some ten seconds. Recently, an even faster temperature increase is desired, and the power applied to the lamp is a large electric power. This is called ‘spike annealing’. The temperature is increased with a speed of more than 200° C. per second, and when the target temperature has been reached, a cooling is performed immediately. By means of this spike annealing an extremely thin diffusion layer (shallow junction) can be formed and the properties of the semiconductor element can be improved.
Devices wherein a plurality of filament lamps is arranged in parallel are utilized for such light irradiation type heating devices. Because filament lamps, although being non-contact heaters, have the ability to respond with a high speed and can heat up to a high temperature instantaneously, they are suited as light sources for the high-speed heating in semiconductor production processes. But if a part of the filament lamps installed in a light irradiation type heating device suffers a wire breakage and becomes non-lighting, the temperature distribution of the semiconductor wafer becomes uneven and there is the risk that a so-called ‘slip’, that is, a defect of crystal transition, occurs in the semiconductor wafer.
Therefore, it is necessary to detect wire breakages of filament lamps installed in a light irradiation type heating device at an early stage and precisely. But because the emission light of a light irradiation type heating device is extremely strong, it is not possible to detect the wire breakage of only one filament lamp even when measuring using an irradiance meter. And because the irradiated area reaches an extremely high temperature, it is also not possible to arrange irradiance monitors. Therefore, it is necessary to detect wire breakages of the individual filament lamps.
There are several methods for the detection of wire breakages of filament lamps. JP-A-6-65172 discloses a method in which a current transformer is used and a current detection of a circuit connecting a heater wire and an inverter is performed. The current transformer is also referred to as ‘measuring transformer’ and is able to measure the alternating current value. Because the current stops flowing when the wire of a filament lamp breaks, the wire breakage of the filament lamp can be detected by means of the current detection value of the current transformer becoming virtually zero.
In JP-A-2-186581, to detect the wire breakage of a heater, a current detector is connected in series to a circuit connecting the heater and a power source. The numeral value obtained from the current detector and a standard value are compared, and if the detection value is lower than the standard value, the judgement is made that a wire breakage of the heater has occurred.
But because of the necessity of a current transformer for each filament lamp when detecting wire breakages using a current transformer, there is the problem with light irradiation type heating devices in which a plurality of filament lamps is arranged side by side that the device itself becomes large. And as a current transformer is installed for each filament lamp, there is also the problem that the production costs increase.
When a current detector is connected in series to the power supply line connecting the power source and the filament lamps, a resistor is installed in the power supply line to detect the current and a power loss occurs. This is because a voltage is generated by the current detector, energy is consumed by the resistor of the power detector, and an excessive power consumption is caused.